1. Field of the Invention
The present invention relates to a method and a device for manufacturing single crystals by employing the Czochralski Method (CZ method).
2. Description of Prior Art
Substrates of semiconductor components are made of high-purity single-crystal silicon. Production of the substrates of semiconductor components is ordinarily performed by the CZ method. In the single-crystal manufacturing device (see FIG. 8) employing the CZ method, a crucible 8 capable of ascending or descending freely is installed at the central portion of the chamber 2. The crucible 8 consists of a graphite crucible 8a and a quartz crucible 8b accommodated within the graphite crucible 8a. Polycrystalline silicon in lumps is deposited into the quartz crucible 8b, then the polycrystalline silicon is heated to melt into melted liquid 3 via a heater 5 disposed around the crucible 8. Subsequently, a seed crystal installed within a seed holder 9 is dipped into the melted liquid 3. Afterward, the seed holder 9 and the quartz crucible 8 are respectively driven to rotate in the same or opposite directions. At the same time, the seed holder 9 is lifted to grow a single crystal 7 with predetermined diameter and length.
A heat-shield plate 10 is installed above the melted liquid 3. The heat-shield plate 10 comprises a rim 10a, which is in the shape of a ring and covers the hot zone, and an adiabatic cylinder 10b connected to the inner edge of the heat-shield plate 10. The adiabatic cylinder 10b is in the shape of an upside-down cone which surrounds the single crystal 7 being lifted, and an adiabatic material 6 made of carbon fibers is accommodated therewithin. Furthermore, an adiabatic material 4 is installed on the outer edge of the rim 10a. The heat-shield plate 10 is used for shielding the single crystal 7 from heat radiating from the surface of the melted liquid 3 or the heater 5. The lifting speed of the single crystal 7 can be raised by expediting the cooling of the single crystal 7, which can be achieved by amplifying the temperature gradients in the longitudinal and the radial directions, especially in the region near the solid-liquid boundary. Furthermore, the heat-shield plate 10 plays the role of guiding the inert gas coming from above the chamber 2 into the surroundings of the single crystal 7 and expelling gases hindering single-crystallization, such as SiO, SiO.sub.2, Si, or metal vapors coming from the crucible 8. This can improve the dislocation-free feasibility.
In addition to the above-described, a single-crystal manufacturing apparatus provided with a cylindrical heat-shield plate extending from the top plate of the chamber to the site near the melted liquid is also employed. The heat-shield plate controls the flow of the inert gas coming from above the chamber and shields the heat radiating from, for example, the melted liquid. By this arrangement, the temperature gradients in the region near the solid-liquid boundary can be increased during the lifting operation of the single crystal, and cooling or temperature maintenance in other temperature regions can be attained. Consequently, single-crystallization can be easily performed and single-crystal productivity is elevated (see for example, Japanese Patent Publication No. 02-97478 and 02-97479). On the other hand, in the single-crystal manufacturing apparatus disclosed in Japanese Patent Publication No. 8-239291, amplifying the temperature gradients in the single crystal requires that the lifting speed of the single crystal be raised. Installing a cooling pipe surrounding the single crystal being lifted and forcing coolant liquid to flow therethrough can amplify the temperature gradients.
However, the capability of conventional heat shield plates to shield heat radiating from the heater and the melted liquid is inefficient, therefore it suffers the following problems.
(1) It is impossible to shield heat radiating from the heater and the melted liquid with conventional heat shield plates so as to comply with the temperature gradient variation, which is induced by the length change of the single crystal being lifted, along the longitudinal axis of the single crystal. Therefore, the lifting speed of the single crystals gets slower from the top to the bottom of the crystal, and the productivity of the single crystals is thus reduced.
(2) The heat history of the temperature zones located at different sites of the single crystal will change if the lifting speed alters. Therefore, grown-in defects, and the amount of oxygen precipitation are affected, and the quality along the longitudinal axis of the single crystal can not be made even.
(3) The cooling area of the cooling pipe installed in the single-crystal manufacturing apparatus disclosed in Japanese Patent Publication No. 8-239291 is small, therefore a sufficient cooling effect can not be obtained.
(4) In the single-crystal manufacturing apparatus in which heat shield plates are affixed, the crucible is unable to be raised during the process of melting raw material. Accordingly, the material lying on the bottom of the crucible can not be melted in an efficient way.